It is known that a particulate filter is designed for trapping particulate matter (soot) that may be contained in the exhaust gases produced by an internal combustion engine, typically of a Diesel engine. When the amount of particulate matter accumulated inside the particulate filter exceeds a maximum allowable limit, the particulate filter needs to be cleaned up in order to restore its original efficiency. This activity, which is conventionally referred to as regeneration of the particulate filter, may be performed by operating the internal combustion engine to increase the temperature of the exhaust gases that flow through the particulate filter, so that the exhaust gases heat the particulate filter up to a temperature that causes the accumulated particulate matter to burn off.
However, during the regeneration, the temperature of the particulate filter is affected by other factors, including the heat generated by the combustion of the particulate matter and the heat evacuated by the mass flow rate of exhaust gases that flow through the particulate filter. In particular, the mass flow rate of the exhaust gases is related, among others, to the engine speed, namely to the rotational speed of the engine crankshaft, which determines the number of exhaust strokes performed per unit of time. As a consequence, if the engine speed abruptly decreases during the regeneration of the particulate filter (e.g. drops to idle speed), the cooling effect of the exhaust gases is significantly reduced and the temperature of the particulate filter may increase uncontrollably.
Accordingly, it is desirable to provide a solution for restoring the efficiency of the particulate filter when the internal combustion engine is operating at low engine speed (e.g. at idle speed), while preventing the particulate filter from being subjected to excessive thermal stress.